Unsaturated loessial soils: a sustainable solution for earthworks

Abstract

A large expansion to one of the world's largest processing facilities is located on unsaturated metastable loessial soils. In these soils particles of silt are cemented together by aggregations of clay compounds and carbonate ‘bridges', forming a porous structure that is hard when dry, but liable to change state rapidly and collapse under wetting and a unique stress ‘threshold pressure'. The proposed processing expansion involves construction in phases of a number of large developments, including processing areas, gas reinjection stations, power plants, a waste management unit, and supporting infrastructure including external and internal roads, bridges and residential developments. The construction would require extensive grading and excavations, resulting in earthworks volumes of hundreds of thousands of cubic metres of metastable soils. To date, the material excavated from the completed phases of development has been considered not reusable, and is placed in selected locations around the field. Based on extensive laboratory data including compaction, CBR, strength, deformation and suction, this paper reports on the potential reuse of these site-won loessial soils as earthworks material, thereby significantly adding to the sustainability aspects of the development. The paper proposes moisture content and suction monitoring of loess fill at placement to supplement the standard site control measures.